The present invention relates to a single-side-molded semiconductor device, which includes a wiring substrate having a ball grid array (BGA) arranged on the lower surface and a semiconductor chip molded with a resin encapsulant on the upper surface. The present invention also relates to a method for fabricating the device.
A semiconductor device of the BGA type has been available as a semiconductor device of an area array type. In the BGA type semiconductor device, a semiconductor chip is mounted and molded with a resin encapsulant on the upper surface of a substrate, and ball electrodes are attached to the lower surface thereof.
FIG. 21 is a plan view illustrating a known semiconductor device of the BGA type. FIG. 22 is a bottom view illustrating the known BGA type semiconductor device. FIG. 23 is a cross-sectional view thereof taken along the line XXIIIxe2x80x94XXIII in FIG. 21.
As shown in FIGS. 21, 22 and 23, the known semiconductor device includes a wiring substrate 103, wiring electrodes 101, a semiconductor chip 104, metal fine wires 105, ball electrodes 102 and a resin encapsulant 106. The wiring substrate 103 is made of an insulating resin. The wiring electrodes 101 are formed on the wiring substrate 103. The semiconductor chip 104 is mounted on the wiring substrate 103 with the principal surface of the semiconductor chip 104 facing upward. Electrode pads (not shown) formed on the semiconductor chip 104 and the wiring electrodes 101 are electrically connected to each other with the metal fine wires 105. The ball electrodes 102 are formed on the lower surface of the wiring substrate 103. The resin encapsulant 106 is provided on the upper surface of the wiring substrate 103. The semiconductor chip 104, wiring electrodes 101, metal fine wires 105 and the like are molded with the resin encapsulant 106 on the upper surface of the wiring substrate 103. Although not shown in FIG. 23, external pad electrodes are formed on the lower surface of the wiring substrate 103. The external pad electrodes are electrically connected to the wiring electrodes 101 through the substrate. The ball electrodes 102 are formed on the external pad electrodes.
The known semiconductor device has an approximately rectangular planar shape and the adjacent side faces thereof are perpendicular to each other. The outer shape has been determined so that the fabrication process of the semiconductor device can be simplified.
Also in the known semiconductor device, the ball electrodes 102 attached to the wiring substrate 103 are solder balls. The solder balls are attached to the wiring substrate 103 so that the overall semiconductor device can be highly reliably mounted and bonded onto a motherboard. In addition, as shown in FIG. 22, the ball electrodes 102 are arranged on the lower surface of the wiring substrate 103 in a latticed shape.
Next, the fabrication process of the known semiconductor device will be described. FIGS. 24A and 24B are respectively a plan view and a bottom view illustrating a known wiring substrate. FIGS. 25A and 25B are plan views illustrating a substrate preparation process step and a die bonding process step, respectively, in the fabrication process of the known semiconductor device. FIGS. 26A and 26B are plan views illustrating a wire bonding process step and a resin molding process step, respectively, in the fabrication process of the known semiconductor device. FIG. 27 illustrates a cutting process step in the fabrication process of the known semiconductor device.
As shown in FIGS. 24A and 24B, the multiple wiring electrodes 101 are formed on the upper surface of the wiring substrate, and external pad electrodes 107 are formed on the lower surface of the wiring substrate. The external pad electrodes 107 are electrically connected to the wiring electrodes 101 through the substrate. The ball electrodes will be attached to the external pad electrodes 107 in the subsequent process step. The wiring substrate is a large-sized substrate on which multiple semiconductor chips will be mounted and which will be separated into individual semiconductor devices. The broken lines shown in FIGS. 24A and 24B are cutting lines, which will be used to separate the substrate into the individual semiconductor devices. Also, in each of the regions defined by the cutting lines in FIG. 24, a central area surrounded by each array of the wiring electrodes 101 is a chip mounting area where each of the semiconductor chips is mounted by bonding.
First, the wiring substrate with the structure shown in FIGS. 24A and 24B is prepared in the substrate preparation process step shown in FIG. 25A.
Next, each of the semiconductor chips 104 is bonded, with an adhesive, onto each of the chip mounting areas of the wiring substrate in the die bonding process step shown in FIG. 25B.
Subsequently, the electrode pads (not shown) formed on the principal surface of each of the semiconductor chips 104 and their associate wiring electrodes 101 formed on the wiring substrate are electrically connected to each other with the metal fine wires 105 in the wire bonding process step shown in FIG. 26A.
Then, the members disposed on the upper surface of the wiring substrate, e.g., the semiconductor chips 104, wiring electrodes 101, metal fine wires 105, are transfer-molded with the resin encapsulant 106 in the resin molding process step shown in FIG. 26B. The wiring electrodes 101 and semiconductor chips 104 are indicated by the broken lines in FIG. 26B. However, the metal fine wires 105 are not shown in the figure.
Next, in the cutting process step shown in FIG. 27, the wiring substrate having the upper surface entirely molded with the resin encapsulant 106 is cut along the cutting lines using a rotary blade, thereby obtaining individual semiconductor devices 108 of the BGA type. Hence, the semiconductor devices 108 with the structure shown in FIGS. 22 and 23 can be obtained.
In this example, the wiring substrate is cut, using the rotary blade, along the cutting lines indicated by the broken lines shown in FIGS. 24A and 24B. In this manner, the individual semiconductor devices can be obtained accurately. Normally, the separation by a rotary blade is performed using a dicing machine generally used in the fabrication process of a semiconductor device. Also, in the cutting process step, the wiring substrate is cut from either the lower surface or the resin encapsulant 106 side thereof.
In the subsequent process step, which is not shown, in each of the individual semiconductor devices 108, a solder ball is attached to each of the external pad electrodes 107 formed on the lower surface of the wiring substrate 103. In this manner, the multiple ball electrodes are formed and will be used as external terminals.
The process steps for fabricating the known semiconductor device have been performed in the above-described manner, i.e., the large-sized substrate on which the multiple semiconductor chips can be mounted is used. Then, a large number of semiconductor chips are mounted on the substrate, the associate members are electrically connected via the metal fine wires, and the members disposed on the upper surface of the wiring substrate are molded with the resin encapsulant. Thereafter, the wiring substrate is cut using the rotary blade and separated into the individual semiconductor devices.
However, the known semiconductor device has drawbacks, i.e., the humidity- and stress- resistance of the semiconductor device is low. This might be because neither the semiconductor chip 104 and resin encapsulant 106 nor the wiring substrate 103 and resin encapsulant 106 are sufficiently secured to each other.
For this reason, it is difficult to increase the reliability of the semiconductor device. Particularly, it is important to obtain the reliability of semiconductor devices used in small electronic units such as mobile phones.
An object of the present invention is providing (1) a semiconductor device of the BGA type with reliable humidity resistance, for example, by using a semiconductor chip having an inverted convex cross-sectional shape instead of a semiconductor chip used in the known semiconductor device, and (2) a method for fabricating the device.
An inventive semiconductor device includes: a wiring substrate; a semiconductor chip; an electrode; a connecting member; and an resin encapsulant. The wiring substrate includes a wiring electrode and an external electrode, respectively, on the upper surface and the lower surface of the wiring substrate. The external electrode is to be electrically connected to the wiring electrode. The semiconductor chip includes: a principal surface; a first bottom face which is opposite to the principal surface; and a second bottom face which protrudes from the first bottom face. The semiconductor chip is mounted on the wiring substrate with the second bottom face being in contact with the upper surface of the wiring substrate. The electrode is formed on the principal surface the semiconductor chip. The connecting member is used to connect the electrode of the semiconductor chip and the wiring electrode formed on the wiring substrate electrically to each other. The resin encapsulant molds the semiconductor chip, the connecting member and the wiring electrode on the upper surface of the wiring substrate. A part of the resin encapsulant exists between the first bottom face of the semiconductor chip and the upper surface of the wiring substrate.
According to the present invention, a part of the resin encapsulant exists between the first bottom face of the semiconductor chip and the wiring substrate. Thus, the semiconductor device can have its humidity resistance improved and also can have its stress resistance to impact from the outside, improved. Accordingly, the highly reliable semiconductor device can be obtained.
In one embodiment of the present invention, a concave portion may be formed in the upper surface of the wiring substrate. Also, the wiring electrode may be formed outside the concave portion. And the second bottom face of the semiconductor chip may be in contact with the bottom face of the concave portion of the wiring substrate. In such an embodiment, the semiconductor device can have its reliability improved further.
In another embodiment of the present invention, in the semiconductor chip, a protrusion length of the second bottom face from the first bottom face is preferably equal to or less than 50% of a thickness of the semiconductor chip.
In still another embodiment, the second bottom face is preferably located approximately in a center region of the back face of the semiconductor chip.
In still another embodiment, the device may further include a ball electrode which is attached to the external electrode of the wiring substrate. Then, the semiconductor device can be mounted on a motherboard more easily.
An inventive method for fabricating a semiconductor device includes the step of a) preparing a wiring substrate, which includes a wiring electrode and an external electrode, respectively, on the upper surface and the lower surface of the wiring substrate. The external electrode is to be electrically connected to the wiring electrode. The method further includes the step of b) preparing a semiconductor chip. The semiconductor chip includes: a principal surface; a first bottom face which is opposite to the principal surface; and a second bottom face which protrudes from the first bottom face. An electrode is formed on the principal surface. The method further includes the step of c) mounting the semiconductor chip on the wiring substrate with the second bottom face secured to the upper surface of the wiring substrate. The method further includes the step of d) connecting the electrode of the semiconductor chip and the wiring electrode on the wiring substrate electrically to each other with a connecting member. And the method further includes the step of e) molding the semiconductor chip, the connecting member and the wiring electrode on the upper surface of the wiring substrate so that a part of a resin encapsulant exists between the first bottom face of the semiconductor chip and the upper surface of the wiring substrate.
According to the present invention, a highly reliable semiconductor device can be fabricated more easily.
In one embodiment of the present invention, the step b) may further include the sub step of: b1) forming, in a semiconductor wafer, chip regions defined by cutting lines. Each of the chip regions has an integrated circuit disposed on the principal surface of each said chip region. The step b) may further include the sub step of b2) forming a groove in a region of the back face of the semiconductor wafer. The region is located at both sides of each of the cutting lines. And the step b) may further include the sub step of b3) separating the semiconductor wafer along the cutting lines into the chip regions, thereby obtaining semiconductor chips, each of which has the first bottom face and the second bottom face. The first bottom face is a part of the bottom face of the groove, and the second bottom face is a part of the back face of the semiconductor wafer. In such an embodiment, a semiconductor chip, which has an inverted convex cross-sectional shape when mounted on a wiring substrate, can be fabricated more easily.
In another embodiment of the present invention, in the step a), a concave portion may be formed in the upper surface of the wiring substrate and the wiring electrode may be disposed outside the concave portion. Also in the step c), the semiconductor chip may be secured to the bottom face of the concave portion of the wiring substrate. Then, a semiconductor device with even higher reliability can be fabricated.
In this particular embodiment, in the step a), the concave portion of the wiring substrate preferably has a depth equal to or less than 40% of a thickness of the semiconductor chip.